Upcycling of Spent LiFePO₄ Cathodes to Heterostructured Electrocatalysts for Stable Direct Seawater Splitting

The pursuit of carbon-neutral energy has intensified the interest in green hydrogen production from direct seawater electrolysis, given the scarcity of freshwater resources. While Ni-based catalysts are known for their robust activity in alkaline water oxidation, their catalytic sites are prone to rapid degradation in the chlorine-rich environments of seawater, leading to limited operation time. Herein, we report a Ni(OH)₂ catalyst interfaced with laser-ablated LiFePO₄ (Ni(OH)₂/L-LFP), derived from spent Li-ion batteries (LIBs), as an effective and stable electrocatalyst for direct seawater oxidation. Our comprehensive analyses reveal that the PO₄³⁻ species, formed around L-LFP, effectively repels Cl⁻ ions during seawater oxidation, mitigating corrosion. Simultaneously, the interface between in situ generated NiOOH and Fe₃(PO₄)₂ enhances OH⁻ adsorption and electron transfer during the oxygen evolution reaction. This synergistic effect leads to a low overpotential of 237 mV to attain a current density of 10 mA cm⁻² and remarkable durability, with only a 3.3 % activity loss after 600 h at 100 mA cm⁻² in alkaline seawater. Our findings present a viable strategy for repurposing spent LIBs into high-performance catalysts for sustainable seawater electrolysis, contributing to the advancement of green hydrogen production technologies.